The present invention relates to a sheet-like light source device. More particularly, the present invention relates to a sheet-like light source device of edge-light type which is employed as a light source in a liquid crystal display device.
A liquid crystal panel is generally so arranged that liquid crystal material is pinched between two opposing substrates and that voltage is selectively impressed onto the liquid crystal material. The transmittance of light is controlled for each pixel by arranging the panel in such a manner, for instance, that pixel electrodes comprising transparent conductive films aligned in a matrix-like manner are provided on at least either of the substrates and that switching elements such as transistors for selectively impressing voltage on each of the pixel electrodes are provided.
Since the liquid crystal panel itself is not capable of emitting light, it is generally required that a light source, that is, a back light is provided on a rear surface thereof to make the panel function as a display. There are conventionally known liquid crystal display devices wherein light-conducting plates are disposed on display surfaces of liquid crystal panels and further employing sheet-like light source devices of edge-light (side-light) type wherein light sources (such as fluorescent tubes) are disposed on edges of the light-conducting plates for the purpose of achieving downsizing which is an important feature of liquid crystal panels.
An example of such a sheet-like light source device is illustrated in FIG. 15 (see FIG. 5 of Japanese Unexamined Patent Publication No. 152577/1997). In FIG. 15, 51 denotes a light-conducting plate, 52 convex portions provided on lateral sides of the light-conducting plate 51, 53 a white-colored retention member, and 54 concave portions provided on the retention member 53 to fit the convex portions 52 of the light-conducting plate 51. 55 denotes a light-incident portion wherein a tubular light source (cold cathode tube) 56 is disposed in proximity thereof.
According to such a sheet-like light source device, it is possible to realize a liquid crystal display device of narrow frame edge with improved mechanical strength against impact in which degradations in luminance in proximities of both ends of the tubular light source might be restricted.
In such a sheet-like light source device, light which is emitted from light source 56 is made incident to the light-conducting plate 51 through the light-incident portion 55 and is propagated through the light-conducting plate 51. In this process of propagation, light is scattered by means of a light-scattering means provided on a reflecting surface or an emitting surface of the light-conducting plate 51 to emit from the emitting surface. In order to improve luminance of the emitting surface, the retention member 53 is generally formed of white-colored material exhibiting a high surface reflectance. The retention member 53 serves to reflect light which did not emit from the emitting surface of the light-conducting plate 51 but from side surfaces of the retention member 53 for returning the same to the light-conducting plate 51.
In a conventional sheet-like light source device, abnormal emission of light will occur on surface portions of the emitting surface located remote from the light-incident portion of the convex portions 52, which might lead to degradations in display qualities. This fact will be explained now with reference to FIGS. 16 to 17. FIG. 16 is a perspective view of the convex portion 52 on the right-hand side of the light-conducting plate 51 of the sheet-like light source device, and FIG. 17 is a perspective view of the concave portion 54 on the right-hand side of the retention member 53.
In FIG. 16, light which is made incident from the light-incident portion 55 of the light-conducting plate 51 is propagated through the light-conducting plate 51 while a part thereof is outgoing from the surface portion 52a of the emitting surface located remote from the light-incident portion 55 in a direction as indicated by the arrow as emitting light 60. As further illustrated in FIG. 17, the outgoing light 60 is scattered by a surface portion 54a of the concave portion 54 of the retention member 53 which opposes the surface portion 52a of the convex portion 52 of the light-conducting plate 51.
Since such scattered light 61 is recognized as partial irregularities in luminance (abnormal emission of light) in proximities thereof, which will be a cause to degrade the display quality when used as a display.
The present invention has been made in view of the above facts, and it is an object thereof to provide a sheet-like light source device which is free of abnormal emission of light and free of degradations in luminance.
In accordance with the present invention, there is provided a sheet-like light source device of edge-light type comprising at least a light source, a light-conducting plate and a retention member for retaining the light-conducting plate, wherein at least one convex portion or concave portion is provided on a lateral surface portion of the light-conducting plate other than a light-incident portion with the light-conducting plate being held in a specified positional relationship by means of the retention member formed with a concave portion or a convex portion which fits with the convex portion or concave portion of the light-conducting plate, and wherein a light-absorbing means is provided on at least a surface portion of either surface of the concave portion or convex portion of the retention member which opposes the light-incident portion of the light-conducting plate.
In accordance with the present invention, there is also provided a sheet-like light source device of edge-light type comprising at least a light source, a light-conducting plate and a retention member for retaining the light-conducting plate, wherein at least one convex portion or concave portion is provided on a lateral surface portion of the light-conducting plate other than a light-incident portion with the light-conducting plate being held in a specified positional relationship by means of the retention member formed with a concave portion or a convex portion which fit with the convex portion or concave portion of the light-conducting plate, and wherein a light-transmitting means is provided on at least a surface portion of either surface of the concave portion or convex portion of the retention member which opposes the light-incident portion of the light-conducting plate.
In accordance with the present invention, there is farther provided a sheet-like light source device of edge-light type comprising at least a light source, a light-conducting plate and a retention member for retaining the light-conducting plate, wherein at least one convex portion or concave portion is provided on a lateral surface portion of the light-conducting plate other than a light-incident portion with the light-conducting plate being held in a specified positional relationship by means of the retention member formed with a concave portion or a convex portion which fit with the convex portion or concave portion of the light-conducting plate, and wherein a light-absorbing means is provided on at least a surface portion of a light emitting surface of either surface of the concave portion or convex portion of the light-conducting plate.